1. Field of the Invention
The present invention relates to a light processing structure for a digital light processing (DLP) projection device; specifically, it relates to a light processing structure for a DLP projection device with a plurality of digital micro-mirror devices (DMD).
2. Descriptions of the Related Art
FIG. 1 shows a schematic diagram of a digital light-processing projector of Taiwan patent application number 93101928. The application was filed by the applicant of this invention on Jan. 29, 2004. The digital light processing projector mainly comprises a color combination module 200, a light source 300, a color separation module 400, three digital micro-mirror devices 500R, 500G, 500B, and a projection lens 600.
The light source 300 emits a light W to the color separation module 400 through an integration rod 310. The color separation module 400 is used for splitting the light W into three colors R, G and B. Dichroic mirrors 402 and 404 split the color lights R, G and B. Color lights R, G and B are incident to the color combination module 200 through the condenser lens 406, 408 and 410 and reflection mirrors 412, 414, 416, 418, 420 and 422. Color light B is reflected onto an incident plane 242a, while color light G is reflected onto an incident plane 232a. Each color light, R, G and B, is first reflected onto the digital micro-mirror devices 500R, 500G 1′and 500B via air gaps of the total internal reflection (TIR) prisms 220a, 230a and 240a and then reflected and directed through the TIR prisms 220a, 230a and 240a. The projection lens 600 is disposed on the light path of each color light, R, G and B behind the color combination module 200. The back focal length 550 is the back focal length of the projection lens.
Light is an electromagnetic wave and can be analyzed as S and P polarization. The S polarization is normal to the plane constructed by the light progressing direction and the normal of the reflection plane. The P polarization direction is parallel to the plane constructed by light progressing direction and the normal of the reflection plane. When the S and P polarized lights pass through an optical coating layer of the color separation module or the color combination module, the spectrum distribution of the S and P polarized lights will have a wavelength shift if the incident angle thereof is not perpendicular to the optical coating layer. When the incident angle is perpendicular to the optical coating layer, it is called zero degree incidence. The larger the incident angle, the larger the wavelength shift will be.
One of the existing problems in conventional technologies is that the wavelength shift of the aforementioned S and P polarized lights while color separation are inconsistent with that of the S and P polarized lights while color combination. Accordingly, light loss occurs. Another existing problem in the conventional technologies is that the color combination module of 3-chip DLP projectors is assembled by an X-prism in conjunction with three TIR prisms. Consequently, the prisms are larger in volume and weight, thereby adding to the cost. Furthermore, other prior art has developed a DLP projection device with two pieces of DMDs (not shown). This technology adopts both a color wheel as a color separation system for two of the three primary colors and a Philip prism in combination with TIR prisms for the color separation and combination systems. Since this technology uses the one Philip prism for both color separation and combination, not only does the prism have a larger volume and weight, but its projection lens also has a longer back focus length. As a result, there are more difficulties in designing the lens.
According to the above descriptions, the light processing structure of the aforementioned DLP projection device for color separation and combination needs to be redesigned for easier assembly, smaller volume, and lighter weight, as well as consist of more saturated colors to increase product quality.